Field of the Invention
The present invention relates to a solid-state image sensor, and more particularly to a solid-state image sensor that is used for a digital camera or the like.
Description of the Related Art
Recently, demands for a camera that can simultaneously acquire a moving image and a still image are increasing. Generally, in order to acquire a smooth moving image, it is desirable to capture images with an exposure time equivalent to the read frame rate of a solid-state image sensor. For a still image, on the other hand, it is preferable to set an exposure time corresponding to the speed of the motion of the object. This means that two types of pixel signals with different exposure times must be acquired to simultaneously acquire a still image and a moving image. To simultaneously acquire a moving image and a still image having a same brightness, the sensitivity of a pixel must be varied according to the duration of the exposure time, since the quantity of light that enters a pixel is in proportion to the exposure time. In a technique proposed in Japanese Patent Application Laid-open No. 2004-120391, a plurality of photoelectric converters having different aperture ratios are disposed in a pixel, and a different exposure time is set for each photoelectric converter, whereby a pixel signal for a moving image and a pixel signal for a still image can be acquired from each photoelectric converter.
Patent Document 1: Japanese Patent Application Laid-open No. 2004-120391.